docs: def get_cameras_battery_level(self):
          """Return a list of battery levels of all cameras."""
          battery_levels = {}
          if not self.camera_properties:
              return None
  
          for camera in self.camera_properties:
              serialnum = camera.get('serialNumber')
              cam_battery = camera.get('batteryLevel')
              battery_levels[serialnum] = cam_battery
          return battery_levels